Phosphate castablesrefer to phosphoric acid or phosphate-bound castables, and the hardening mechanism is related to the type of binder used and the way of hardening. The binding agent of the phosphate castable can be phosphoric acid or a mixed solution of aluminum dihydrogen phosphate formed by the reaction of phosphoric acid and aluminum hydroxide. At room temperature, the binder and aluminum silicate materials generally do not react (except iron). It needs to be heated to make the binder dehydrate and condense, and the aggregate powder is adhered and cemented, so as to obtain the strength at room temperature.
When a coagulant is used, no heating is required, and magnesia fine powder or high alumina cement can be added for coagulation. When magnesium oxide fine powder is added, it reacts rapidly with phosphoric acid to form, causing the refractory to coagulate and harden, and when aluminate cement is added, it forms phosphates with good gelling properties, hydrous phosphates such as calcium monohydrogen phosphate or diphosphate Calcium hydrogen, etc., cause the material to coagulate and harden.
From the hardening mechanism of phosphoric acid and phosphate refractory castables, it can be known that only when the reaction speed between the binder and the refractory aggregate and powder is appropriate during the heating process, an excellent refractory castable can be formed. However, in the process of re-grinding, ball milling and mixing, the refractory raw materials are easy to bring in impurities such as metal iron, which will react with the binder to release hydrogen during mixing, resulting in bulging of the refractory castable, loose structure, and reduced compressive strength. This is unfavorable for the production of ordinary phosphoric acid and phosphate refractory castables.
